1. Technical Field
The present invention relates to optical signal processors, and more particularly to a programmable system and method for analyzing optical spectral data from an image.
2. Discussion
Image gathering systems are capable of sensing and storing high-quality images of objects with extremely high resolution. When such systems are located at remote locations (particularly in mobile systems), the data gathered thereby must often be transmitted to a base receiver. However, often the data gathering capabilities of the imaging system usually exceeds its ability to transfer this data over conventional data links. Because of this, serious compromises must be made in deciding what data to transmit and what to discard.
This is a serious limitation in many areas such as earth monitoring satellites (eg. LANDSAT) which are capable of acquiring much more data than they can feasibly transmit to the ground. To deal with this problem, imaging instruments in the satellite typically will send down the spectral intensity of an image integrated over a small number of bands of wavelength in order to ease the burden on the downlink. For example, the imaging instrument may integrate over a region of the spectrum and transmit a single number that indicates the average radiance over that region. The entire spectrum may be reduced to five data points representing the radiance in five wavelength bands. This results in a serious loss of information present at wavelengths not included in the bands selected, as well as loss of information other than the average intensity of the spectral signature inside the bands. This degraded information may then be transmitted to the ground and used to identify areas in the scene by their spectral signatures. Of course, this identification is limited by the incompleteness of the information.
Moreover, the particular wavelength bands chosen must be fixed on the ground before the satellite is launched and cannot be changed thereafter. As a result, the wavelength bands chosen often represent a compromise between the competing demands and desires of a number of groups desiring to use the spectral information. For example, these groups may include oceanographers, arctic ice mappers, mineralogical exploration teams, groups performing agricultural mapping, and organizations mapping oil spills. Each of these groups would like to have the data transmitted in spectral bands tailored to their particular applications. The bands actually chosen generally represent a compromise which is not ideal for any of these applications. Since the small number of spectral bands (which typically may be six) are incorporated into the system by means of physical optical filters, they cannot be changed after the satellite is deployed and the users must simply make the best of the compromise bands.
Thus, it would be desirable to provide an image processing system which permits changes to be made in the spectral analysis of an image without altering the physical hardware. Also, it would be desirable to provide such a system in which the nature of the optical spectral analysis is programmable, so that it can be altered from a remote location.
In addition, it would be desirable to provide an image processing system which permits the utilization of all available information to perform target recognition. Further, it would be desirable to provide such a system which can significantly compress the gathered image data without sacrificing useful information when performing target recognition. Also, it would be desirable to provide a system with the above features which is relatively light, inexpensive and suitable for use in systems such as satellites.